Optimisation of protection, to keep radiological exposures as low as reasonably achievable (ALARA), taking into account social, economic and, more recently, environmental circumstances, has been central to radiological protection for decades. However, due to scientific uncertainties and remaining gaps in knowledge on the biological effects of exposure to low doses of ionising radiation on human and ecosystem health, minimisation of dose has often been substituted for a robust optimisation process. The objective of the NEA Workshop on Optimisation: Rethinking the Art of Reasonable was to discuss the nature and intention of optimisation of radiological protection, and how reasonableness should be interpreted and applied in practice. The workshop participants agreed that the prevailing circumstances that give rise to radiological and other risks or hazards are complex, multidimensional and multidisciplinary. The optimal protection solution should be selected based on a broad understanding of the prevailing circumstances and of the positive and negative consequences of each protection solution considered. Such a holistic approach, which takes into account radiological, economic, societal, lifestyle, etc. aspects, was considered most likely to optimise the well-being of populations directly and indirectly affected by circumstances and protection decisions. To facilitate this evolution, the workshop focused on protection by addressing well-being in its broadest sense. It is therefore important to recognise that radiological protection is only one of the factors to be taken into account in optimising overall well-being and may, in fact, focus efforts on radiological health risks to the detriment of other risks. In contrast, the goal of optimising well-being can focus overall protection solutions on the most serious issues, allocating resources in a more risk-prioritised fashion.